Process of producing pure chromium by electrolysis



- heretofore employed.

formed .by such processes have scaled off Patented June 10, 1924.

. UNITED STATES 1 4 6,845 E T OFFICE.

GEORG GRUIBE, OF STUTTGART, GERMANY, ASSIGNOR TO METAL & TH ERMIT CORPO'RA .TION, OF CHROME, NEW JERSEY, A CORPORATION OF -INEVY' JERSEY.

PROCESS OF PRODUCING PURE OHROMIUM. BY ELECTROLYSIS.

No Drawing.

To all whom it camera Be it known that I, Gnone GRUBE, a citizen of the German'Republic, residing at Stuttgart, Germany, have invented certain new and useful Improvements in Processes of Producing Pure Chromium by Electrolysis (for which I have filed an application in Germany on July 19, 1921, and for-which further applications have been filed by as signees as follows: Czechoslovakian Republic, September 23, 1922; Switzerland, September 23, 1922; Sweden, September 23, 1922; Austria, September 25, 1922; Norway,

September 27, 1922; Great Britain, Septemhe 28-1922;

Belgium, October 17, 1922; Ital October 24, 1922; and France, October specification.

Pure chromium,'free of carbon, has been manufactured heretofore principally by aluminothermical means or in the electric furnace. Attempts have been made to produce chromium metal by electrolysis, but it has not been possible to produce thick precipitates of uniform density in a re liable manner by means of the processes The precipitates after. reaching a certain thickness or have been deficient 1n uniformity or otherwise .unfit for use.

The present invention relates to an electrolytic process by means of which not only thin but also thick deposits of pure chr0- mium may be produced in a continuous manner, said process involving the use of an electrolytic bath containin as initial ingredients chromium trioxid iOr O'Q, chromic hydrox'id (Ci-(0H),), an an acid other than chromic acid capable of dissolving chromic 'hydroxid, the amount of chromium trioxid bein equal to at least twice the amount of the chromic hydroxid and. the acid together. In order to obtain satisfactory results the chromic hydroxid content of the bath should be in excess of the quantity necessaryto neutralize the acid content of the bath.

The deposition of the chromium may be effected upon any kind of metallic parts,

- such for example upon iron or copper or upon nickel coated iron. As an anode leadof which the following is a Application filed April 13, 1923. Serial no. 631,906.

-mium produced at the cathode and not reduced to metal nor being obtained in metallic condition, are subjected to a higher degree of oxidation at the anode with formation of chromium-trioxid.

The process may for instance be carried out in the. following manner: Into an electrolytic decomposition vessel filled with water a sufficiency of chromium-trioxid, sulphuric acid and chromic 'hydroxid are introduced that in each liter of the solution;

there are contained 250 g. CrO 3 g. Cr,-(SO,) and 6g. Cr(OH)-,. Such'a solution is obtained by using for each liter of water 2.50 g. ,CrO 2.25 g. H SO, and 7.58 g. Cr(OH) The solution is submitted to electrolysis at the temperature of the room without the use of a diaphragm. and at a current density of 10 amp. per square decimeter at the cathode, and a current density of 5 amp. per square decimeter at the'anode. Thus for instance a' current 015.32 to 3.4 volts and 30 amp. current strength was employed with two lead-hyperoxid anodes of about 3 square decimeter each active surface and in parallel connection between which the cathode of 3 square decimeter surface consisting of copper sheet was sus pended. -During the procedure CrO, in solid condition was added in such a manner that the contents of the electrolyte of CI2(SO4)3 and Cr(O-H) remained unchanged and that only the chromic acid was reduced to metallic chromium. Under the conditions mentioned in 100 hours 300 g. pure chromium were precipitated for which purpose 577 g.- CrO, had to be introduced into the solution. g

-The operation could be carried on for months continuously and yielded layers of chromium of any desired'thickness; it was even possible to obtain the precipitated chromium in a highly glossy condition.

- The chromium adheres with considerable tenacity to a chromium-coated piece of sheet rillia-nt chromium precipitates upon. a'

polished carrier of someother metal-such "as iron, copperor'lbrass, so that the objects which have been coated with chromium in this manner may be directly employed withcipitated upon the metallic chromium ,thus' out any subsequent polishing. llt is evident moreoverQthatother metalsmay be preproduced by electrolysis, so that such metals will firmly adhere thereto. hand, the surface of a cathode may be prepared by well known means, by 'Very slight greasing for instance, so that a layer of chromiumprecipitated thereon may be readily detached.

f'coated metals preferably in an 'indifi'erent or inert gas the different metals may be alloyed .with each other completely or to any desired extent. 7

It should be pointed out that my invention is not restricted tothe particular proportions, current'densities and conditions hereintofore referred to, but that such con ditions and percentages may varyto suit existing conditions and other changes and modifications may be made in accordance with localrequirements and the convenience ofthe operator, and without deviatingfromthe spirit of my invention as pointed outthanchromic acid capable I of forming a I soluble chromium salt by reaction with chromic hydroxid, the chromium trioxid being equal to at least twice the total amount of-the chromic hydroxid and acid.

.lProcess of producing pure metallic chromium which consists in electrolyzing a solution formed by. mixing water, chromiumtrioxid, chromic hydroxid, and an acid other than chromic acid capable of forming a soluble chromium salt by reaction with chromic hydroxid, the chromium trioxid being equal to at least twice the total amountof the chromic hydroxid and acid,

and the chromic hydroxid being in excess of the quantity necessary for the neutralization of the acid.

chromic hydroxid and a soluble chromium salt, the total amount of the chromic' hydroxid and chromium salt being less than half of the amount of the chromium in the bath.

0n, the other trioxid me iate aqueous bath containihg chromium triorid, chromic hydroxid and a soluble chromium salt, the chromium trioxid being equal to at least twice the amount of the chromic cathode. By the subsequent heating of chromium 5. The process of producing pure metallic chromium which consists in electrolyzing an aqueous bath, containing chromium trioxid, chromichydroxid and chromic sulphate the total; amount of the chromic hydroxid and of the chromic sulphate being less than half the amount of the chromium trioxidpresent.

6. Process of producing pure metallic chromium which consists in electrolyzing an equeous bath containing chromium trioxid,

chromic hydroxid and a soluble chromium salt, the chromium 't'rioxid being equal to at leasttwice the amount of the chromic hydroxid and chromium salt, and regulating the 'currentdensities at the electrodes so as to produce anodic oxidation into chromium trioxid of the lower oxides of chromium for-med atthe cathode.

I 'LProcess of producingpure metallic I chromium which consists in elect-rolyzing an aqueous bath containing chromium 'trioxid, .chromic hydroxid and a soluble chromium salt, the chromium trioigid being equal .to at least twiceth'e amountof the chromic the current. densities to approximately ten amp'eres per square decimeter at the cathode and approximately five amperes per squarev decimeter at the anode. f-

tion during the electrolysis at a rate cor- Y responding to the rate of deposition of metallic chromium, and. correspondingly regulating the relative current densities at the electrodes, thereby maintaining the composition of the bath substantially unchanged during the electrolysis.

p mom.

in testimony whereof, afhx my signal 7 "ture, A f' 1 a. Process of producing pure metallic chromium which consists'in electrolyzing an hydroxid and chromium salt, and regulating v lOO 

